1. Field of the Invention
The invention relates to a paper calender with a stack of rolls arranged one above the other. The stack of rolls includes of an upper stack and a lower stack that can each individually be placed under load by upper and lower force generators. The stack also has a common center roll that is supported on the calender's frame, and remaining center rolls that are carried on levers capable of pivoting about axes fixed with respect to the frame and that are capable of being placed under load by force applying devices. The invention also relates to a method for operating the calender.
2. Discussion of Background Information
A calender is known from German Patent No. DE 195 11 145 A1. In this calender, a common center roll is a flexible, adjustable roll with a cover (casing, jacket or shell) lift having a cover supported on a carrier that passes through the cover and is fixed with respect to the frame. The cover is also supported by an upper support apparatus that can be compressively loaded and a lower support apparatus so that it can be compressively loaded. The paper web is fed such that one side of it in the upper stack and the other side of it in the lower stack comes into contact with hard rolls that are responsible for the smoothness of the paper. With the aid of a force applying device the weight of associated parts can be compensated for. As a result of the roll weight, the load characteristic curves have a negative slope in both the upper stack and the lower stack, i.e. the line loads increase from top to bottom from gap to gap.
Known from International Patent Publication No. WO 95/14813 is a paper calender with a roll stack in which all center rolls located between an upper and a lower end roll are carried on levers. These levers can be placed under load by devices that apply force. The devices are designed to be powerful enough to be capable of compensating for more than the total weight of the roll and the parts connected to it. In this way, load characteristic curves with positive slope can be achieved as well as those with negative slope.
However, in both cases it is difficult to give the paper web approximately the same surface consistency on both sides.